Process for preparing benzotrifluoride and its derivatives

ABSTRACT

A process for preparing benzotrifluoride or derivatives thereof by contacting benzotrichloride or the corresponding derivatives with hydrogen fluoride in a gaseous phase in the absence of any catalyst, the contact being carried out in the presence of chlorine at an elevated temperature so as to accelerate the reaction rate.

This is a continuation-in-part application of our copending applicationSer. No. 859,755 filed Dec. 12, 1977.

The present invention relates to a process for preparingbenzotrifluoride and its derivatives. More particularly, it relates toan improved process for preparing benzotrifluoride or a derivativethereof by reaction of benzotrichloride or the derivative correspondingthereto with hydrogen fluoride in the gaseous phase.

For preparation of benzotrifluoride from benzotrichloride and hydrogenfluoride, there have been known various procedures, none of which issatisfactory from the industrial viewpoint. For instance, the procedurefor reacting benzotrichloride with hydrogen fluoride in the liquid phaseat a temperature higher than 80° C. (cf. U.S. Pat. No. 1,964,244;Japanese Patent Publication (unexamined) No. 77324/1975) results in theformation of hydrogen chloride as a by-product during the reaction,whereby the pressure is much elevated. Accordingly, care must be takenconcerning the stability in operation and the safety in working. Inaddition, an expensive high pressure reaction apparatus is needed. Inorder to avoid the above drawbacks, a procedure for carrying out thereaction by introducing benzotrichloride gradually into hydrogenfluoride in the liquid phase at a temperature lower than 19° C. underatmospheric pressure (cf. U.S. Pat. No. 3,136,822) has been proposed.However, this procedure has the disadvantage that a considerably longperiod of time for completion of the reaction is required. Besides,there are known numerous other procedures wherein the reaction ofbenzotrichloride with hydrogen fluoride is carried out in the presenceof various catalysts (cf. U.S. Pat. No. 3,950,445). However, theseprocedures are disadvantageous in necessitating such catalysts for thereaction, showing only a lower conversion in the reaction underatmospheric pressure and requiring a long period of time for completionof the reaction.

Because of various drawbacks and disadvantages as seen in the proceduresfor carrying out the reaction of benzotrichloride with hydrogen fluoridein the liquid phase, attempts have been made to effect such a reactionin the gaseous phase in the absence of any catalyst. In this procedure,however, the reaction rate is extremely low so that benzotrifluoride cannot be efficiently produced even at an elevated temperature.

As the result of an extensive study, it has now been found that thereaction of benzotrichloride with hydrogen fluoride in the gaseous phasein the absence of any catalyst can be remarkably accelerated in thepresence of chlorine. It is notable that the remarkable enhancement ofthe reaction rate is produced under substantially atmospheric pressure.The present invention is based on the above finding.

According to the present invention, there is provided a process forpreparing benzotrifluoride or a derivative thereof which comprisescontacting benzotrichloride or a derivative corresponding thereto withhydrogen fluoride in the presence of chlorine in the gaseous phase at anelevated temperature.

In the process of this invention, the starting material isbenzotrichloride or a derivative thereof (hereinafter referred to as"benzotrichloride compound"). As the derivative of benzotrichloride,there may be used any compound having a chemical structure constitutedwith a benzene ring and at least one trichloromethyl group thereon. Inaddition to at least one trifluoromethyl group, one or more substituentswhich do not materially interfere with the reaction between thetrichloromethyl group and hydrogen fluoride may be optionally present onthe benzene ring. Examples of such substituents are nitro, cyano,halogen (e.g. chlorine, bromine, iodine), etc. Thus, the term"benzotrichloride compound" includes those of the formula: ##STR1##wherein R₁, R₂ and R₃ are each hydrogen, trichloromethyl, nitro, cyanoor halogen, provided that one of R₁, R₂ and R₃ is nitro, each of theother two not being nitro.

The molar ratio of hydrogen fluoride to be used to the benzotrichloridecompound may be usually from about 3 to 15, preferably from about 3.3 to12. The molar ratio of chlorine to the benzotrichloride compound isnormally not more than about 0.3, preferably from about 0.02 to 0.2. Theuse of chlorine in a higher amount than the said upper limit does notproduce any advantage and may be rather unfavorable in producing a lossof the space or capacity.

In carrying out the process of the present invention, designed amountsof the benzotrichloride compound, of hydrogen fluoride and of chlorine(which is usually dissolved in the benzotrichloride compound to make asolution) may be charged, for instance, in a pre-heating apparatus andheated to make a gaseous mixture. The gaseous mixture is introduced intoa reactor having a tubular shape, whereby the reaction proceeds at anelevated temperature. The reaction mixture exhausted from the reactor isintroduced into a distillation tower, and gaseous materials such ashydrogen chloride, hydrogen fluoride and chlorine are taken out from thetop of the tower while liquid materials including the producedbenzotrifluoride or its derivative are obtained from the bottom of thetower.

The reactor may be made of any material resistant to corrosion byhydrogen fluoride, hydrogen chloride, chlorine and the like at anelevated temperature. Examples of such materials are stainless steel,nickel, nickel alloys (e.g. Inconel, Hastelloy), etc.

The elevated temperature in the reactor is varied with the kind of thebenzotrichloride compound and may be usually from about 250° to 600° C.,preferably from about 300° to 500° C. The contact time in the reactor isnot limitative but is usually at least about 0.2 second, preferably notmore than about 10 seconds. A higher temperature or a longer contacttime over the said upper limits will unfavorably result in the increasedproduction of tars or by-products. The pressure in the reactor isusually atmospheric but may be reduced or elevated.

The thus obtained liquid materials comprise benzotrifluoride or itsderivative (hereinafter referred to as "benzotrifluoride compound"),which corresponds to the starting benzotrichloride compound. Thederivative of benzotrifluoride may be the one having a chemicalstructure constituted with a benzene ring and at least onetrifluoromethyl group thereon. In addition to at least onetrifluoromethyl group, one or more substituents such as nitro, cyano,halogen and the like may be present on the benzene ring. Thus, the term"benzotrifluoride compound" includes those of the formula: ##STR2##wherein R₁ ', R₂ ' and R₃ ' are each hydrogen, trifluoromethyl, nitro,cyano or halogen, provided that one of R₁ ', R₂ ' and R₃ ' is nitro,each of the other two not being nitro.

Recovery of the benzotrifluoride compound from the liquid materials maybe carried out by a per se conventional separation procedure such asdistillation.

The process of this invention is industrially advantageous in producingbenzotrifluoride or derivatives thereof efficiently in high yieldswithout using any expensive reacton apparatus even under atmosphericpressure.

Practical and presently preferred embodiments of the invention areillustratively shown in the following Examples wherein % and part(s) areby weight unless otherwise indicated.

EXAMPLES 1-6 AND COMPARATIVE EXAMPLES 1-2

Designed amounts of p-chlorobenzotrichloride (hereinafter referred to as"p-ClBTC"), m-nitrobenzotrichloride (hereinafter referred to as "m-NO₂BTC" or benzotrichloride (hereinafter referred to as "BTC") containingchlorine previously dissolved therein and of hydrogen fluoride arecharged in a pre-heating apparatus, and the contents are heated to about280° C. The resulting gaseous mixture is introduced into a "Hastelloy C"made tubular reactor (inner volume, 150 ml) with regulation of the feedamount, and the reaction is effected under the conditions as shown inTable 1. The reaction product coming out of the reactor is transferredto a distillation tower and distilled there.

From the top of the distillation tower, low boiling impurities such ashydrogen chloride, hydrogen fluoride and chlorine are exhausted, andfrom the bottom of the tower, the residual liquid substances areobtained. This liquid is subjected to gas chromatographic analysis(stationary phase: Silicone SE 30; column, 3 m; temperature-elevatingrate, 5° C./min). The results are shown in Table 1.

For comparison, the reaction is effected in the same manner as above butnot using chlorine. The results are also shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                 Reaction conditions                                                                        HF/p-ClBTC                                                            Cl.sub.2 /p-ClBTC                                                                     or m-NO.sub.2 BTC                                   Starting     Tempera-                                                                           or m-NO.sub.2 BTC                                                                     or BTC  Contact                                     p-ClBTC      ture or BTC  (molar  time Reaction products (mol %)              Example                                                                             or BTC (°C.)                                                                       (molar ratio)                                                                         ratio)  (sec.)                                                                             F.sub.0                                                                         F.sub.1                                                                         F.sub.2                                                                         F.sub.3                                                                         Remarks                        __________________________________________________________________________    1     p-ClBTC                                                                              300  0.052   5.0     3.5  40                                                                              15                                                                              18                                                                              27                               2     p-ClBTC                                                                              298  0.075   5.2     3.6  11                                                                              24                                                                              25                                                                              40                               3     p-ClBTC                                                                              298  0.15    5.5     3.2  10                                                                              18                                                                              27                                                                              46                               4     p-ClBTC                                                                              400  0.052   5.9     2.8   0                                                                               4                                                                              26                                                                              70                               5     p-ClBTC                                                                              500  0.052   5.8     1.7   0                                                                               1                                                                               1                                                                              98                               6     BTC    400  0.052   5.8     2.7   0                                                                               1                                                                               2                                                                              97                               7     m-NO.sub.2 BTC                                                                       410  0.052   6.0     2.3   0                                                                               0                                                                               2                                                                              98                               Compara-                                                                            p-ClBTC                                                                              301  0       4.9     3.6  43                                                                              34                                                                              20                                                                               3                                                                              Tars ob-                       tive 1                                         served in                      Compara-                                                                            p-ClBTC                                                                              400  0       5.6     1.8  21                                                                              22                                                                              43                                                                              14                                                                              the reactor.                   tive 1                                                                        __________________________________________________________________________     Note:                                                                         ##STR3##                                                                     - -                                                                            ##STR4##                                                                 

What is claimed is:
 1. A process for preparing benzotrifluoridederivatives which comprises contacting a benzotrichloride compound ofthe formula:wherein R₁, R₂ and R₃ are each hydrogen, trichloromethyl,nitro, cyano or halogen but wherein all of R₁, R₂ and R₃ are nothydrogen at the same time and when one of R₁, R₂ and R₃ is nitro, eachof the other two is not nitro, with hydrogen fluoride in the absence ofany catalyst in the gaseous phase and in the
 2. The process according toclaim 1, wherein the hydrogen fluoride is used in a molar ratio of about3 to 15 with respect to the benzotrichloride
 3. The process according toclaim 1, wherein the chlorine is used in a molar ratio of not more thanabout 0.3 with respect to the
 4. The process according to claim 1,wherein the contact is effected at a
 5. The process according to claim1, wherein the contact is effected for a
 6. The process according toclaim 1, wherein R₁, R₂ and R₃ are each hydrogen, trichloromethyl orhalogen.